A Phase I Trial Using a Multitargeted Recombinant Adenovirus 5 (CEA/MUC1/Brachyury)‐Based Immunotherapy Vaccine Regimen in Patients with Advanced Cancer

Lessons Learned Concurrent ETBX‐011, ETBX‐051, and ETBX‐061 can be safely administered to patients with advanced cancer. All patients developed CD4+ and/or CD8+ T‐cell responses after vaccination to at least one tumor‐associated antigen (TAA) encoded by the vaccine; 5/6 patients (83%) developed MUC1‐specific T cells, 4/6 (67%) developed CEA‐specific T cells, and 3/6 (50%) developed brachyury‐specific T cells. The presence of adenovirus 5‐neutralizing antibodies did not prevent the generation of TAA‐specific T cells. Background A novel adenovirus‐based vaccine targeting three human tumor‐associated antigens—CEA, MUC1, and brachyury—has demonstrated antitumor cytolytic T‐cell responses in preclinical animal models of cancer. Methods This open‐label, phase I trial evaluated concurrent administration of three therapeutic vaccines (ETBX‐011 = CEA, ETBX‐061 = MUC1 and ETBX‐051 = brachyury). All three vaccines used the same modified adenovirus 5 (Ad5) vector backbone and were administered at a single dose level (DL) of 5 × 1011 viral particles (VP) per vector. The vaccine regimen consisting of all three vaccines was given every 3 weeks for three doses then every 8 weeks for up to 1 year. Clinical and immune responses were evaluated. Results Ten patients enrolled on trial (DL1 = 6 with 4 in the DL1 expansion cohort). All treatment‐related adverse events were temporary, self‐limiting, grade 1/2 and included injection site reactions and flu‐like symptoms. Antigen‐specific T cells to MUC1, CEA, and/or brachyury were generated in all patients. There was no evidence of antigenic competition. The administration of the vaccine regimen produced stable disease as the best clinical response. Conclusion Concurrent ETBX‐011, ETBX‐051, and ETBX‐061 can be safely administered to patients with advanced cancer. Further studies of the vaccine regimen in combination with other agents, including immune checkpoint blockade, are planned.